The present invention broadly relates to vacuum switches and, more specifically, pertains to a new and improved construction of a vacuum switch having an actuation rod electrically connected to a terminal of the switch.
Generally speaking, the vacuum switch of the present invention comprises a vacuum chamber, a contact actuation rod sealingly conducted out of the vacuum chamber and reciprocatable through a predetermined length of stroke, and electrical terminals which are to be commutated by the vacuum switch. The contact actuation rod is electrically connected to the terminal by a connecting conductor.
One characteristic which distinguishes vacuum switches from switches of other construction for comparable voltages, for instance low oil content switches or gas-blast switches, is the relatively small switching stroke executed by the movable contact member. Among other things, this permits a very compact construction. The actuation rod conducted out of the vacuum chamber and electrically connected with the movable contact member must, however, be connected with one of the stationary terminals of the switch by a connecting conductor, as must other types of switches as well.
In known vacuum switches of the initially mentioned type, for instance as disclosed in the Swiss Patent No. 551,687, and Swiss Patent No. 585,959, the connecting conductor consists of a copper cable or a flexible conductor strap which is usually provided at both ends with soldered terminal connectors which, in turn, are fixedly clamped to the terminal member, on the one hand, and to the actuation rod, on the other hand, by means of threaded connectors. This connecting conductor requires considerable effort to produce and assemble and is, when conducting heavy currents, subject to magnetic forces emanating from such currents, with the result that the position and shape of this connecting conductor can vary within the switch from switch stroke to switch stroke, since the copper cable is very flexible.
Other vacuum switches have adopted constructions for this connecting conductor which are common in switches having considerably greater switch strokes. For instance, the vacuum switches described in the Swiss Patent No. 558,078 comprise encircling slide contacts between the actuation rods leading into the vacuum chamber and the associated terminals. When using such slide contacts, the frictional resistance to be overcome by the switch drive must be very considerable in order to guarantee good contact.
In order to reduce this frictional resistance, the actuation rod in the vacuum switch according to the U.S. Pat. No. 3,997,741, granted Dec. 14, 1976, is surrounded by an irregular, preferably corrugated, sleeve made from a good conducting material and whose inner side contacts the outer side of the actuation rod along one or more of its generatrices. This sleeve, in turn, is surrounded by a stationary tube arranged coaxially with the actuation rod and which is fixedly connected with the terminal. Compressible bars or rods, for instance made of rubber, are inserted between the inner side of the tube and the outer side of the irregular sleeve which tend to hold the irregular sleeve in a deformed configuration and therefore in contact with both the tube and the actuation rod. This construction may well guarantee good contact between the actuation rod and the switch terminal with a low frictional resistance, but it involves a very great constructional expense and is not able to derive any advantage from the short switch strokes characteristic of vacuum switches.
Analogous remarks with respect to constructional effort and insufficient consideration of the characteristically short switching strokes can be made in relation to the U.S. Pat. No. 3,958,093, granted May 18, 1976, in which roller contacts engage the outer surface of the actuation rod.